DE 37 12 628 has disclosed an inner ring for holding guide vanes of a stationary gas turbine. The guide vanes which are arranged in a star shape around the rotor to form a guide vane ring are secured to the housing of the gas turbine by means of their radially outer guide vane roots. The radially extending guide vanes, on their side facing the rotor, have the guide vane head, which is connected to the stationary inner ring. This inner ring, which is U-shaped in cross section, engages coaxially around the rotor of the gas turbine and connects the guide vanes of a guide vane ring to one another in order to increase the stability of the guide vane ring and to improve the vibrational properties of the guide vanes. A gap is in this case formed between the web of the U-shaped inner ring, its flanks and the corresponding circumferential and end faces associated with the rotor. Likewise, the web of the U-shaped inner ring, on its surface facing the rotor, has one half of a labyrinth seal, which together with the second half arranged on the rotor forms the labyrinth seal.
When the gas turbine is operating, the working fluid which flows within the flow passage is only supposed to flow past the guide vanes of a guide vane ring. However, the working fluid can also flow through the gap formed by stationary and rotating components, as a leakage flow.
To reduce the extent of the leakage flow, the gap between the stationary and rotating components is sealed by means of the labyrinth seal.
Furthermore, it is known to provide a plurality of labyrinth seals in the gap between the flank of the inner ring and of the shaft shoulder, in order to achieve an improved sealing action. In this case, two labyrinth seals are arranged axially and radially offset with respect to one another, in a terraced arrangement, in the gap between the flank and shaft shoulder.
The terraced arrangement of a plurality of labyrinth seals takes up a large amount of space and is only used for stationary gas turbines. Stationary gas turbines have a parting plane located between a lower housing half and an upper housing half and are fitted together radially during assembly. In the process, the finished rotor is inserted into the lower housing half, which has already been preassembled and onto which the upper housing half is then fitted, so that only labyrinth seals which are offset in terraced fashion with respect to one another are possible between the rotor and the housing.
U.S. Pat. No. 5,222,742 has disclosed a stacked labyrinth seal between the securing ring for the guide vane of a turbine and a rotor blade mounted on the rotor of the turbine. The turbine is an axially assembled aircraft turbine, i.e. the axially successive rotor blade rings and guide vane rings of the individual compressor stages and/or turbine stages are mounted in succession ring by ring, so that a stacked arrangement is possible. Further labyrinth seals which have been stacked in this way for aircraft turbines are known from DE 199 31 765 and FR 2 241 691.
Since stacked labyrinth seals have hitherto only been known for aircraft turbines, a person skilled in the art was not hitherto in a position to transfer stacked labyrinth seals to stationary gas turbines, on account of the axial method of assembly.